Various devices have in the past been used to visually indicate the presence of suspended cables, and in particular suspended high voltage wires. The devices used in the past on high voltage wires have been of various shapes such as spherical, substantially conical, or of shapes such as those disclosed in U.S. Pat. No. 3,253,571 issued to Williams. Typically, such devices have been made of plastics such as fibreglass although they can be made of sheet metal as in indicated in the Williams patent. These prior devices were either directly connected to the high voltage wire, such as those disclosed in the Williams patent and U.S. Pat. No. 3,662,377 to Helm, or suspended from the high voltage wire by means of a suspension apparatus such as that disclosed in U.S. Pat. No. 3,135,236 to Pfeiffer et al. The suspension apparatus is usually made of metal. The disadvantage of these earlier markers is that when they were made from a nonconducting material such as fibreglass or other plastic, they suffered from a corona discharge from either the high voltage wire itself, when the marker was mounted directly on the wire, or from the usually metallic suspension apparatus when the marker was suspended from the high voltage wire by means of such an apparatus. Of course, even if a sufficiently strong nonconducting suspension apparatus could be used, a corona discharge could occur from the high voltage wire into the suspension apparatus itself. Over a period of time, the corona discharge would eventually destroy the plastic material from which the marker was made, as well as cause other side effects such as radio and television interference. As corona discharge is a phenomena which is directly dependent upon voltage gradient, the severity of the corona discharge problem increases with voltage for a conductor of given shape, and increases with the presence of sharp points or edges on a conductor attached to a source of given voltage. On high voltage wires with voltages in the order of 500 thousand to 1 million volts, the corona discharge problem becomes particularly severe.
Where metallic markers of a shape such as the sheet metal markers described in the patent to Williams are used, corona discharge still presents a problem as a result of the presence of sharp edges. Such sheet metal markers if they are to be of appreciable size would also be unduly heavy and thereby cause an unacceptable mechanical strain on the high voltage wire. As well, markers such as those disclosed in the patent to Williams, due to the method by which the marker is directly attached to the high voltage wire, tend to cause further strain on that wire by prohibiting the natural mechanical oscillations of the wire. In addition, such markers made of sheet metal are not sufficiently flexible so as to withstand mechanical stress resulting from transmission line mechanical oscillations.
It is desirable to provide a marker for use on a suspended high voltage wire which is both electrically conductive so as to substantially eliminate a corona discharge problem and yet which is sufficiently light so as to be supportable on the wire without causing undue strain on it, and which marker will not be affected by mechanical oscillations of the high voltage wire.